Can anyone explain what the difference is between KEYWORD2 and KEYWORD3 in keywords.txt, for syntax coloring?

I see that there are a few instances of these in the 1.0 release (for setup, loop, and a few Serialn keywords), but I can't find any documentation on it and don't understand the distinction that is being made.

The entries for the IDE display of them in preferences.txt look like:

editor.keyword1.style=#cc6600,plain

editor.keyword2.style=#996600,plain

editor.keyword3.style=#993300,bold

But I don't see setup and loop appearing in that keyword3 color or in bold, in any case. It's a slightly darker brown than keyword2.